Interpretive Summary: Starches are widely used in industry where its physicochemical and functional properties require dissolution or dispersion in water solutions without undergoing degradation. Since starches do not dissolve in water, organic solvents or strong alkali have been used for the dissolution of starch granules for the characterization of starches. Recently, it was reported that starches dissolve in water at high temperature/high pressure. In this report, we showed that starch molecules degrade in water at high temperature and the degree of degradation depends on the heating temperature. This means that the temperature of starch solution needs to be carefully controlled to obtain a product with desired properties. For non-food applications, moderately degraded starches can be used as an alternative stabilizer for the production of nanoparticles. Dextran, a conventionally used stabilizer, is very expensive (~$1,000/lb).
These results will benefit scientists in academia investigating physicochemical properties of starch and industries that process starch products in water.

Technical Abstract:
Starches are not soluble in neutral water at room temperature. However, if they are heated in a closed container beyond the boiling point of water, they eventually dissolve. The dissolution temperature depends on the type of starch. The dissolution process was monitored in real time by measuring the transmittance of starch dispersion/solution while it was heated. It was found that the dissolution of starches in water results from the degradation of the two components of starches, amylopectin and amylose. Although the molecular structure of repeating units of the two components are the same, amylopectin was more susceptible to degradation than amylose, leading to the conclusion that the a(1'6) glycosidic bonds of the glucose repeating unit unique to amylopectin are weaker than the a(1'4) bonds.